1. Field of the Invention
The invention relates to reversible, crosslinked, orientable liquid crystalline (LC) polymers based on LC poly(meth) acrylates PP, which are suitable for optical data storage, or for coatings or laminations with special anisotropic optical properties, wherein the poly(meth)acrylate can be the substrate of a self-supporting film or foil usable for special optical applications and a method of manufacturing the same.
2. Background of the Invention
In the area of information storage, LC polymers are of great interest (see Allen, G., and Bevington, J., 1989, "Comprehensive Polymer science", V. 5, pub. Pergamon Press, pp. 701-732). Anisotropic, thin LC polymer films may be oriented using various methods, thereby converting them to LC monodomains. This orientation can be accomplished, e.g., by:
electromagnetic fields (see EP 0,231,856=U.S. Pat. No. 4,886,718; EP 0,231,857=U.S. Pat. No. 4,837,745; and EP 0,231,858=U.S. Pat. No. 4,896,292);
surface effects (DE 38 25 066);
mechanical deformation (see Finkelmann, H., and Hammerschmidt, K., 1989, Makromolo Chem., 190, 1089-1101).
In general the macroscopic orientation is carried out at a temperature range between the glass temperature (T.sub.g) and the clear temperature (T.sub.n' i) of the polymer. In the case of LC side chain polymers the temperatures at which orientation is carried out are near the clear temperature.
EP 0,410,205 describes a method of manufacturing self-supporting anisotropic LC polymer films based on photo-crosslinked poly(meth) acrylates. These films are suitable for, e.g., optical data storage. The anisotropic LC polymer film can be converted to a macroscopically oriented anisotropic state by mechanical deformation, without a support material.
However, in orienting anisotropic, thin LC polymer films by electromagnetic fields or by surface effects, one is limited to structured support materials and specific film thicknesses. According to DE 38 25 066, films which are 1-2 .mu.m thick can be oriented without problems. However, these methods come up against operable limits at a film thicknesses above 10 .mu.m. Films of thickness &gt;10 .mu.m are prepared as a rule by the "display" technology, which involves substantial thermal stress on the polymers. A third method is mechanical deformation (i.e. shear stressing, stretching, and compressing) which is used for orienting LC main chain polymers and crosslinked LC polymers (see Zentel, R., Finkelmann, H., et al., in Gordon, M., Ed., 1984, "Advances in polymer science", V. 60/61, pub. Springer Verlag, of Heidelberg, pp. 155-162; and Finkelmann, H., et al., 1987, Mol. Cryst. Liq. Cryst., 142, 85-100).
Orientation of LC elastomers is carried out, in a manner analogous to that of linear side chain polymers, below the clear temperature T.sub.n' i (the temperature for transition from nematic to isotropic phase) in the rubberelastic state, and is frozen-in below the glass temperature T.sub.g. Because crosslinked LC elastomers, such as polysiloxanes (other than the cyclic tri- and tetra-monomers), have very low glass temperatures, substantially below room temperature, the orientation is preserved only under stressing or at low temperatures below the T.sub.g of the elastomer.
EP 0,410,205 describes a method of manufacturing LC poly(meth)acrylates with incorporated photo-crosslinking groups, and the use of such polymers for manufacturing anisotropic LC selfsupporting polymer films, as well as applications of such films. These films are formed from an organic solvent, which must be disposed of, and the films are irreversibly crosslinked, and are no longer thermoplastic.
Accordingly, the problem of devising reversibly crosslinkable LC polymers which can be thermoplastically processed in the non-crosslinked state, oriented by means of known methods, and which at below certain temperatures, can form self-supporting crosslinked LC polymer films remains.